Inrush-current limiting device

ABSTRACT

Apparatus, associated with an inverter circuit, for limiting inrush-current into a storage capacitor during an initial charging period, while minimizing the power dissipation of the limiting device during normal inverter operation. A resistive element provides a limiting device for the initial charging period of the storage capacitor. A silicon-controlled rectifier with associated apparatus, placed in a conducting state by the operation of the inverter circuit, provides an alternate low impedance path in parallel with the resistive element following the initial charging period.

United States Patent 1191 Potter INRUSII-CURRENT LIMITING DEVICE [75]Inventor: Geoffrey Potter, Hopkinton, Mass.

[73] Assignee: Honeywell Information Systems Inc.,

Waltham, Mass.

22 Filed: Jan. 2, 1973 21 Appl. 110.; 320,038

[ Dec. 25, 1973 3,227,940 1/1966 Gilbert et al 321/11 3,401,327 I 9/1968Leppcrt 321/45 8 Primary ExaminerWilliam M. Shoop, Jr. Attorney-WilliamW. Holloway, Jr. et al [57] ABSTRACT Apparatus, associated with aninverter circuit, for limiting inrush-current into a storage capacitorduring an 52 11.5. CI 321/11 321/45 s initial charging P Whileminimizing the POWer 51 1m. (:1. ..1i02m 1/18 P= of the limiting deviceduring normal 58 Field of Search 321/11 45 s Veiter Operation Aiesisiive element ProvideS a limiting device for the initial chargingperiod of the storage [56] References Cited capacitor. Asilicon-controlled rectifier with associated apparatus, placed in aconducting state by the UNITED STATES PATENTS operation of the invertercircuit, provides an alternate 3,334,290 8/1967 Landls 321/11 limpedance path in parallel with the resistive 3 ment following theinitial charging period. 216261378 1/1953 Levy, .lr... 321/45 S 25Claims, 2 Drawing Figures F 52 CONTROL APPARATUS 1' 6| l 7 r3 1 1 W lv,l

l 53 I50 5| 5e 11 1 1 162 127 q l 6O PATENTEDHEIIZS ma SHEET 1 BF 2INRUSH-CURRENT LIMITING DEVICE BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates generally to power supplies and,more particularly, to apparatus in a power supply having an invertercircuit, for limiting a surge of (inrush-)current during a start-upperiod while minimizing the continuing power losses due to the apparatuslimiting the inrush-current.

2. Description of the Prior Art Methods for limiting an initial surge ofcurrent during the start-up of a circuit, such as a power supply, whichrequires the charging of a storage capacitor, are known in the priorart. The limiting of the inrush-current is necessary because the storagecapacitor, being initially uncharged, is the instantaneous circuitequivalent of short circuit as seen by the input power source. Thepresence of a short circuit, even momentarily, can result in largecurrent transients, damaging the circuit elements carrying theinrush-current unless the elements are capable of handling highcurrents. However, elements capable of handling these high currents areexpensive, and provide capability that is not required during the majorportion of the circuit operation.

It is therefore known in the prior art to provide a resistor between theinput power source and the storage capacitor to limit the inrush-currentsurge into the circuit. However, the continued presence of the resistorprovides a continuing source of power loss which, for high poweroperations, can prove to be unacceptable.

In order to minimize the power loss due to the limiting resistor, aswitch can be provided in parallel with the resistor. The switch can beoperated either manually or automatically, the automatic operationresponding typically to a passage of time, to conditions of the outputvoltage, or to conditions in the apparatus controlling the operation ofthe circuit. The switch, when activated, provides analternative lowimpedance path for input current during normal operation. The prior artmanual and automatic switching apparatus is either unresponsive topotentially damaging fault condition or is unduly complicated. Incircuits in which the above problems are found, an inverter circuit,that isa circuit for changing a DC voltage to an AC voltage, isfrequently present. (The operation of an inverter circuit is describedin Silicon Controlled Rectifier Manual; F.W. Gutzwiller, Editor; GeneralElectric Company; Auburn, N.Y., 1961, 2nd Edition; or in SemiconductorControlled Rectifiers: Principles and Applications of p-n-p-n Devices,F.E. Gentry, F.W. Gutzwiller, N. Holonyak, .lr., and BE. Von Zustraw;Prentice-Hall, Inc.; Engle Wood Cliffs, New Jersey; i964.) The presenceof the inverter circuit allows use of an inrush-current limiting devicewhich provides a solution for the above-discussed problems.

OBJECTS It is therefore an object of the present invention to provide animproved power supply.

It is a further object of the present invention to provide for limitingthe inrush-current into a storage capacitor.

It is a still further object of the present invention to provide aresistor for limiting the current surging into a storage capacitorduring start-up of the circuit while providing an alternate lowimpedance path during the circuits, normal operation.

It is another object of the present invention to provide simpleapparatus for by-passing a limiting circuit element during normaloperation of an associated inverter circuit.

It is still another object of the present invention to provide a simpleinrush-current limiting device for a power supply containing an invertercircuit.

These and other features of the invention will be understood uponreading of the following description together with the drawings.

SUMMARY OF THE INVENTION The aforementioned and other objects of thepresent invention are accomplished by providing an electronic switch inparallel with the impedance limiting the current initially charging astorage capacitor. The electronic switch provides an electrical path forbypassing the limiting impedance during normal operation of an invertercircuit.

The electronic switch is a silicon-controlled rectifier (SCR) coupled inparallel with the limiting resistor. The gate terminal of the SCR iscoupled to the inverter circuit. The operation of the invertingapparatus provides a continuously renewed bias of the SCR gate terminalrelative to the SCR cathode terminal resulting in continuing theconducting state of the SCR during normal inverter operation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagramof a power supply, containing associated inverter circuitry, with atypical inrush-current limiting impedance according to the prior art.

FIG. 2 is a schematic circuit diagram of the power supply of FIG. 1 withthe addition of the inrush-current limiting device of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Description of the ApparatusReferring now to FIG. 1, terminal T1 and terminal T2 receive power froman input power source. The input power source typically suppliesrectified, but unregulated voltage to terminals T1 and terminal T2.Terminal T1 is coupled to a first terminal of impedance 140. Impedanceprovides the inrush-current limiting device for the power supply and isshown as a resistor in FIG. 1. A second terminal of impedance 140 iscoupled to terminal T2 through capacitor 51 and resistor 127, connectedin parallel. Capacitor 51 is the storage capacitor of the power supply,while resistor 127 provides an electrical path for a slow discharge ofthe capacitor 51, such as when the power supply is switched off.Resistor 127 is commonly called a bleeder resistor.

The second terminal of the impedance 140 is also coupled to an anode ofSCR 54. The cathode of SCR 54 is coupled to one terminal of aprimarywinding of a transformer 55. A second terminal of the primarywinding of transformer 55 is coupled, through capacitor 52, to thesecond terminal of impedance 140. A gate terminal of SCR 54 is coupledthrough resistor I14 and capacitor 113, connected in parallel, to thecathode of SCR 54. The gate terminal and the cathode terminal of SCR 54are also coupled to control apparatus.

A first terminal of the secondary winding of transformer 55 is coupledto terminal T4. A second terminal of the secondary windingof transformer55 is coupled to the anode of diode 59. A cathode of diode 59 is coupledthrough capacitor 60 to terminal T4, and through inductance 61 toterminal T3. Terminal T3 is also coupled to terminal T4 throughcapacitor 62. In the preferred embodiment, transformer 55 has more thanone secondary winding, and-in that event, each first terminal of thesecondary windings is coupled to terminal T4, while each second tenninalof the secondary windings of transformer 55 is coupled through diodes inparallel to diode 59 to the first terminal of inductance 61.

A second terminal of the primary winding of transformer 55 is coupledthrough capacitor 53 to terminal T2, and to a first terminal of aprimary winding of transformer 57. A second terminal of the primarywinding of transformer 57 is coupled to an anode of SCR 56. The cathode.of SCR 56 is coupled to terminal T2, the gate terminal of SCR 56is-coupled through resistor 1 17 and capacitor 116, connected inparallel, to the cathode of SCR 56. The gate element and the cathodeelement SCR 56 are also coupled to the control apparatus.

A first terminal of a secondary winding of transformer 57 is coupled toterminal T4 while a second terminal of the secondary winding oftransformer 57 is coupled to a anode of diode 58. The cathode of diode58 is coupled to inductance 61. Transformer 57 can have more than onesecondarywinding. A first terminal of each secondary winding-is in thatevent, coupled to terminal T4, while a second terminal of each secondarywinding of transformer 57 is coupled through diodes, connected inparallel to'diode 58 to inductance 61.

In the prior art, a manually operated switch, or an electricallyoperated switch controlled by the status of either the control apparatusor the output voltage.

across terminals T3 and T4, can be connected across impedance 140 inorder to bypass that element during normal operation of the powersupply.

Referring now to FIG. 2, the additional apparatus necessary, accordingto the present invention, to by- Pa s th u bur cpt limi ing de i e, isshown- In FIG. 2, resistor 120 provides the inrush-current limitingdevice during the initial charging of capacitor 51. Terminal T1 iscoupled to ananode element of SCR 101. The cathode terminal of SCR 101is coupled to a second terminal of resistor 120. Thus when SCR 101 is ina conducting state the resistor 120 is effectively shortcircuited. Thegate terminal of SCR 101 is coupled to the cathode terminal of SCR 101through resistor 102 and capacitor 103, connected in parallel. The gateterminal of SCR 101 is coupled also to a cathode terminal of diode 104.The anode of diode 104 is coupled through resistor 105 to the secondterminal of the primary winding of transformer 55. Resistor 120,resistor 105, resistor 102, diode 104 capacitor 103 and SCR 101 comprisethe inrush-current limiting device and are labelled 150 in FIG. 2.

Operation of the Preferred Embodiment Referring once again to FIG. 1,the input unregulated power source is coupled between terminal T1 andtertransformer 55. (A detailed. description ,of the operation of controlapparatus for a power supply similar to that found in FIG. 1 and FIG. 2is found in Patent application Ser. No. 320,041 assigned to the assigneeof the instant Invention.) The control apparatus provides a relativelybrief biasing voltage before being removed by the control apparatusfTheinductive nature of transformer 55 causes an amount of charge to betransferred to capacitor 53 in excess of the quantity of chargeoriginally stored on capacitor 52. When the current flowing through SCR54in the positive direction becomes sufflciently small, SCR 54 becomesnon-conducting in the absence of a biasing signal. The current throughthe primary winding of transformer 55 causes current to flow through thesecondary circuit of transformer 55. Elements 60, 61 and 62 provides afilter for this current rectified through diode 59. A DC voltage is thusapplied between terminals T3 and T4.

After SCR' 54 stops conducting, the control apparatus provides apositive pulse to the control gate of SCR 56 relative to the cathodeelement ofSCR 56. Thus, SCR 56 becomes conducting and capacitor 53' isdischarged through the primary winding of transformer 57. Accordingly,current flowing in the secondary winding of transformer 57 providesadditional, current through diode 58, for the filter coupled to theoutput of that transformer. Thus, additional current is contributed formaintaining the voltage acrossterminals T3 and T4. By alternatelyswitching SCR 54 and SCR 56 to the conducting state with a highrepetition rate, the ripple voltage across terminals T3 and T4 can bemade small.

The operation of a power supply opertion in the man ner described aboveis called a DC to DC converter (cf Silicon Controlled Rectifier Manualor Semiconductor Controlled Rectifiers, cited supra).

Referring next to FIG. 2, while charge is being stored on capacitor 51,the current is limitedby resistor 120, SCR 101 being in a non-conductingstate. With the operation of the inverter circuit comprising SCR 54 andSCR 56, the voltage applied to the gate terminal relative to the cathodeterminal of SCR 101 becomes positive, causing SCR 101 to assume aconducting state and thereby by-passingresistor 120. Each time SCR 54becomes conducting thereafter, a positive voltage is applied to gateterminal relative to the cathode terminal of SCR 101, causing SCR 101 tobe in the conducting state.

The resistor 102 and resistor are in a series circuit'when the gateterminal becomes positive relative to the cathode terminal of SCR 101.Thus, resistor 102 and resistor 105 provide a resistance dividingnetwork protecting the gate terminal of SCR.104 from exceeding to highvoltage differencerelative to the cathode terminal of SCR 101. Diode 104prevents current from flowing in a reverse direction from the gateterminal of SCR 101.

The presence of capacitor 103 provides a means for maintaining positivevoltage on the gate terminal relative to the cathode terminal of SCR-101during the interval between consecutive conducting states of SCR 54.Further if a ripple voltage across terminals T1 and T2 is large, butoccurs with a frequency slow compared to the operation of the invertercircuit, the elements may be chosen for SCR 101 to remain conducting fora time determined by consecutive peaks of the ripple voltage.

In the above described embodiment an inductive load was provided for theSCR 54 and SCR 56 by a transformer. It is clear that inductiveimpedances can be used in place of these two transformers. In case thatan inductive load is used, a transformer, preferrably with a relativelylow power drain may be coupled between terminal T2 and the couplingbetween the two inductive elements replacing transformer 55 andtransformer 57. (The detailed operation of such a power supply isdescribed in co-pending Patent application Ser. No. 320,047, assigned tothe assignee of the instant Invention). An important feature is that thereactive nature of the impedance in series with the SCR (54) provides anexcess amount of charge to be transferred between capacitors, permittingthe gate terminal of SCR 101 to become positive periodically relative tothe cathode element. When SCR 54 is not alternating between theconducting and the non-conducting state, the positive voltage betweenthe gate terminal and the cathode terminal of SCR 101 will not bemaintained and the silicon-controlled rectifier will becomenonconducting when a sufficiently low current flows between the anodeand the cathode element.

The suspension of operation of the inverter circuit, as for example withthe detection of a fault condition by the control apparatus, providesfor the removal of the biasing voltage for SCR 101. Thus SCR 101 canassume a non-conducting state and reinstatement of resistor 120 inseries with the input power source provides circuit element protection.The gate terminal of SCR 101 is coupled directly to the inverter circuitand complex feedback apparatus such as required when the SCR 101 iscoupled to other portions of the power supply are eliminated.

The above description is included to illustrate the operation of thepreferred embodiment and is not meant to limit the scope of theinvention. The scope of the invention is to be limited only by thefollowing claims. From the above discussion, many variations will beapparent to oneskilled in the art that would yet be encompassed by thespirit and scope of the invention.

What is claimed is;

1. An electrical power supply comprising:

a current limiting resistor coupled to a first power supply inputterminal;

a first storage capacitor coupled between said current limiting resistorand a second power supply input terminal;

a second storage capacitor coupled to said first storage capacitor;

means for charging said second storage capacitor comprising a firstinductive impedance and a first electronic switch coupled in series withsaid first inductive impedance, said charging means coupled between saidcurrent limiting resistor and said second capacitor, said charging meansoperating in response to a first control signal;

means for discharging said second storage capacitor comprising a secondinductive impedance and, a second electronic switch coupled in series,said discharge means coupled between said second capacitor and a secondpower supply input terminal, said discharge means operating in responseto a second control signal;

means for controlling said charging means and said discharging means,said control means producing alternately said first control signal andsaid second control signal;

means for producing a rectified and filtered output signal, said outputmeans coupled to at least one of said first and said second inductiveimpedance; and

a third electronic switch coupled in parallel with said current limitingresistors said third electronic switch coupled to said second storagecapacitor, said third electronic switch being conductive during acharging of said second storage capacitor.

2. The power supply of claim 1 further comprising:

means for maintaining said third electronic switch in a conducting statefor a preselected time after a charging of said storage capacitor.

3. The power supply of claim 2 wherein said third electronic switchincludes a silicon-controlled rectifier and wherein a gate terminal ofsaid silicon-controlled rectifier is coupled to said second storagecapacitor.

4. The power supply of'claim 3 further including:

a third storage capacitor coupled to said first storage capacitor andsaid second storage capacitor, said third storage capacitor beingalternately charged and discharged out of phase with said secondcapacitor.

5. The power supply of claim 4 wherein said conducting state maintenancemeans is a third capacitor coupled between said gate terminal and acathode terminal of said silicon-controlled rectifier.

6. The power supply of claim 5 wherein a first resistor is coupledbetween said gate terminal and said cathode terminal, and wherein asecond resistor connected in series with a diode is coupled between saidgate terminal of said silicon-controlled rectifier and said secondstorage capacitor.

7. The power supply of claim 6, wherein said control means monitors saidoutput signal, an interval of time between said first and said secondcontrol signals determined by said output signal.

8. A electrical power supply comprising:

a first resistor having one terminal coupled to a first power supplyinput terminal;

a first capacitor coupled to said first resistor and coupled to a secondpower supply input terminal;

a first silicon-controlled rectifier (SCR), an anode terminal of saidfirst SCR coupled to said first resistance,

a first inductive impedance coupled to a cathode of said first SCR;

a second SCR coupled to said second input terminal;

a second inductive impedance coupled between said firstinductiveimpedance and second SCR;

a second capacitor coupled between said first and said second inductiveimpedance, and coupled to said second input terminal;

a third SCR, an anode terminal of said third SCR coupled to said firstinput terminal, a cathode element of said third SCR coupled to a saidanode terminal of said first SCR, a gate terminal of said third SCRcoupled to said cathode terminal of said third SCR through a secondresistor and a third capacitor connected in parallel, said gate terminalof said third SCR further coupled to said second capacitor through athird resistor and a diode connected in series;

means for controlling said first and said second SCR, said first SCRbecoming conductive during a first portion of a cycle for said controlmeans, whereby said second capacitor becomes charged, said control meanscausing said second SCR to become conductive during a second portion ofsaid control means cycle, whereby said second capacitor is discharged;and

means for producing an output signal one of said first and said secondSCR coupled to at least one inductive impedance, said output signalproduced in response to signal changes across said inductive impedance.

9. The power supply of claim 8 wherein control means is coupled to saidoutput signal, said output signal determining an interval for saidcontrol means cycle.

10. A power supply comprising:

means for producing a rectified output signal from a time-varyingsecondary signal;

means for'producing a time-varying primary signal, said primary signalmeans coupled to said output signal means for producing said secondarysignal;

an input impedance for limiting current intoflsaid power supply, saidinput impedance coupled to said primary signal means; and

means for by-passing said input impedance, said bypass means directlycoupledto said primary signal means, wherein said by-pass means isactivated by primary signal.

11. The power supply of claim 10, wherein said primary signal meanscomprises at least one inductive impedance and at least one electronicswitch connected in series, wherein charging of conductive andnonconductive states of said electronic switch causes said time-varyingprimary signal.

12. The power supply of claim 11 further comprising a capacitor coupledto said primary signal means, wherein charging and discharging of saidcapacitor is produced by changing of said state of conduction of saidsilicon-controlled rectifier.

13. The power supply of claim 12 further including means for controllingsaid electronic switch, said control means coupled to said outputsignal, wherein said output signal controls a rate of change of saidstates of conductivity of said electronic switch.

14. An improved circuit of the type having a resistor which limitscurrentflowing into a first capacitor, and having a second capacitor,said second capacitor being alternately charged through a firstinductive impedance and discharged through a second inductive impedance,wherein the improvement comprises:

a switching device coupled in parallel with said resistor, wherein acontrol terminal of said switching device is coupled to said secondcapacitor, wherein a charging of said second capacitor causes saidswitching device to assume a conducting state.

15. The improved circuit of claim 14 wherein the improvement furthercomprises:

means for maintaining said switching device in a conducting state for atleast a preselected time after charging of said second capacitor.

16. The improved circuit of claim 15 wherein said switching device is asilicon-controlled rectifier and wherein said control terminal is a gateterminal of said silicon-controlled rectifier.

17. The improved circuit of claim 16 wherein said means for maintainingsaid silicon-controlled rectifier in said conducting state comprises acapacitor coupled between said gate terminal and a cathode terminal ofsaid silicon-controlled rectifier.

18. The improved circuit of claim 17 wherein said gate element iscoupled through a first control resistor to said cathode terminal and isfurther coupled through a second control resistorto said secondcapacitor, said first and second control resistor forming a resistancedividing network for protection of said siliconcontrolled rectifier.

19. The improved circuit of claim 18 wherein said silicon-controlledrectifier gate is coupled through a diode to said second capacitor, saidsecond diode preventing a reverse current from flowing from said gateterminal. v

20. In a circuit in which a state of at least one electronic switch isrendered alternatively conducting and non-conducting, wherein changed insaid electronic switch state cause a varying current in an inductiveelement, said current composed of charge extracted from a storagecapacitor, said currentapplied to an output circuit, wherein said outputcircuit provides a steady output voltage in response to said varyingcurrent, an input devicecomprising:

a resistor coupled between said storage capacitor'and an input powersource, said resistor'limiting current flowing from said power source tosaid capacitor, and

a silicon-controlled rectifier (SCR) coupled in parallel with saidresistor, a gate of said SCR coupled to said inductive element, whereinsaid varying current causes said SCR to assume a conducting state.

21. The circuit of claim 20 wherein said gate is coupled to saidinductive element through a first control resistor and a diode andwherein said gate is coupled to a cathode of said SCR through acapacitor and a second control resistor, said capacitor and said secondcontrol resistor connected in parallel, wherein said capacitor causessaid SCR to remain in a conducting state for a preselected time after analternation in said state of said electronic switch, and wherein saidfirst and second control resistors prevent excessive voltage betweensaid gate and said cathode.'

22. A circuit comprising:

a storage capacitor; I I

,a limiting resistor coupled to said storage capacitor for limitingcurrent flowing into said storage capacitor;

a switch element coupled in parallel with said limiting resistor,wherein activation of said switch element causes said switch element tobe in a conducting state, said conducting state of said switch elementproviding an electrical path for by-passing said limiting resistor; and

an inverter circuit for changing a DC signal to an AC signal, saidinverter circuit coupled to 'said storage capacitor, wherein saidstorage capacitor provides said DC signal to said inverter circuit, saidinverter circuit coupled to said switch element, wherein operation ofsaid inverter circuit causes said switch element to be in saidconducting state.

23. The circuit of claim 22 wherein said switch element includes asilicon-controlled rectifier, wherein a gate terminal of said SCR iscoupled to said inverter circuit.

24. The circuit of claim 23 wherein said switch element furthercomprises a capacitor coupled between said gate terminal and a cathodeterminal of said sili said gate terminal and said cathode terminal andwherein said switch element further comprise a second resistor and adiode couple between said gate terminal and said inverter circuit.

, UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3:781637 Dated December 25, 1973 Inventor s) Geoffrey Potter It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 8, line 17, delete "changed" and insert -changes-.

Signed and sealed this 21st day of May 1974.

(SEAL) Attest: v

EDWARD M.FLETCHER,JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents F ORM PC3-1050 (10-69) USCOMM-DC 60376-Pc9 a u.s. GOVERNMENTrnmrms ornc: n19 0-366-S3A,

v UNITED sTATEs PATENT OFFICE CERTIFICATEv OF CORRECTiON Patent No.3,781,637 Dated December 25, 1973 Inventor(s) G r y Potter It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 8, line 17, delete "changed" and insert --changes--.

Signed and sealed this 21st day of May 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PC7-1050 (10-69) USCOMM DC eoflhpw w as. sovnuyzm rnmnusornc: ID! o-us-su.

1. An electrical power supply comprising: a current limiting resistorcoupled to a first power supply input terminal; a first storagecapacitor coupled between said current limiting resistor and a secondpower supply input terminal; a second storage capacitor coupled to saidfirst storage capacitor; means for charging said second storagecapacitor comprising a first inductive impedance and a first electronicswitch coupled in series with said first inductive impedance, saidcharging means coupled between said current limiting resistor and saidsecond capacitor, said charging means operating in response to a firstcontrol signal; means for discharging said second storage capacitorcomprising a second inductive impedance and, a second electronic switchcoupled in series, said discharge means coupled between said secondcapacitor and a second power supply input terminal, said discharge meansoperating in response to a second control signal; means for controllingsaid charging means and said discharging means, said control meansproducing alternately said first control signal and said second controlsignal; means for producing a rectified and filtered output signal, saidoutput means coupled to at least one of said first and said secondinductive impedance; and a third electronic switch coupled in parallelwith said current limiting resistors said third electronic switchcoupled to said second storage capacitor, said third electronic switchbeing conductive during a charging of said second storage capacitor. 2.The power supply of claim 1 further comprising: means for maintainingsaid third electronic switch in a conducting state for a preselectedtime after a charging of said storage capacitor.
 3. The power supply ofclaim 2 wherein said third electronic switch includes asilicon-controlled rectifier and wherein a gate terminal of saidsilicon-controlled rectifier is coupled to said second storagecapacitor.
 4. The power supply of claim 3 further including: a thirdstorage capacitor coupled to said first storage capacitor and saidsecond storage capacitor, said third storage capacitor being alternatelycharged and discharged out of phase with said second capacitor.
 5. Thepower supply of claim 4 wherein said conducting state maintenance meansis a third capacitor coupled between said gate terminal and a cathodeterminal of said silicon-controlled rectifier.
 6. The power supply ofclaim 5 wherein a first resistor is coupled between said gate terminaland said cathode terminal, and wherein a second resistor connected inseries with a diode is coupled between said gate terminal of saidsilicon-controlled rectifier and said second storage capacitor.
 7. Thepower supply of claim 6, wherein said control means monitors said outputsignal, an interval of time between said first and said second controlsignals determined by said output signal.
 8. A electrical power supplycomprising: a first resistor having one terminal coupled to a firstpower supply input terminal; a first capacitor coupled to said firstresistor and coupled to a second power supply input terminal; a Firstsilicon-controlled rectifier (SCR), an anode terminal of said first SCRcoupled to said first resistance, a first inductive impedance coupled toa cathode of said first SCR; a second SCR coupled to said second inputterminal; a second inductive impedance coupled between said firstinductive impedance and second SCR; a second capacitor coupled betweensaid first and said second inductive impedance, and coupled to saidsecond input terminal; a third SCR, an anode terminal of said third SCRcoupled to said first input terminal, a cathode element of said thirdSCR coupled to a said anode terminal of said first SCR, a gate terminalof said third SCR coupled to said cathode terminal of said third SCRthrough a second resistor and a third capacitor connected in parallel,said gate terminal of said third SCR further coupled to said secondcapacitor through a third resistor and a diode connected in series;means for controlling said first and said second SCR, said first SCRbecoming conductive during a first portion of a cycle for said controlmeans, whereby said second capacitor becomes charged, said control meanscausing said second SCR to become conductive during a second portion ofsaid control means cycle, whereby said second capacitor is discharged;and means for producing an output signal one of said first and saidsecond SCR coupled to at least one inductive impedance, said outputsignal produced in response to signal changes across said inductiveimpedance.
 9. The power supply of claim 8 wherein control means iscoupled to said output signal, said output signal determining aninterval for said control means cycle.
 10. A power supply comprising:means for producing a rectified output signal from a time-varyingsecondary signal; means for producing a time-varying primary signal,said primary signal means coupled to said output signal means forproducing said secondary signal; an input impedance for limiting currentinto said power supply, said input impedance coupled to said primarysignal means; and means for by-passing said input impedance, saidby-pass means directly coupled to said primary signal means, whereinsaid by-pass means is activated by primary signal.
 11. The power supplyof claim 10, wherein said primary signal means comprises at least oneinductive impedance and at least one electronic switch connected inseries, wherein charging of conductive and non-conductive states of saidelectronic switch causes said time-varying primary signal.
 12. The powersupply of claim 11 further comprising a capacitor coupled to saidprimary signal means, wherein charging and discharging of said capacitoris produced by changing of said state of conduction of saidsilicon-controlled rectifier.
 13. The power supply of claim 12 furtherincluding means for controlling said electronic switch, said controlmeans coupled to said output signal, wherein said output signal controlsa rate of change of said states of conductivity of said electronicswitch.
 14. An improved circuit of the type having a resistor whichlimits current flowing into a first capacitor, and having a secondcapacitor, said second capacitor being alternately charged through afirst inductive impedance and discharged through a second inductiveimpedance, wherein the improvement comprises: a switching device coupledin parallel with said resistor, wherein a control terminal of saidswitching device is coupled to said second capacitor, wherein a chargingof said second capacitor causes said switching device to assume aconducting state.
 15. The improved circuit of claim 14 wherein theimprovement further comprises: means for maintaining said switchingdevice in a conducting state for at least a preselected time aftercharging of said second capacitor.
 16. The improved circuit of claim 15wherein said switching device is a silicon-controlled rectifier andwherein said control terminal is a gate terminal oF saidsilicon-controlled rectifier.
 17. The improved circuit of claim 16wherein said means for maintaining said silicon-controlled rectifier insaid conducting state comprises a capacitor coupled between said gateterminal and a cathode terminal of said silicon-controlled rectifier.18. The improved circuit of claim 17 wherein said gate element iscoupled through a first control resistor to said cathode terminal and isfurther coupled through a second control resistor to said secondcapacitor, said first and second control resistor forming a resistancedividing network for protection of said silicon-controlled rectifier.19. The improved circuit of claim 18 wherein said silicon-controlledrectifier gate is coupled through a diode to said second capacitor, saidsecond diode preventing a reverse current from flowing from said gateterminal.
 20. In a circuit in which a state of at least one electronicswitch is rendered alternatively conducting and non-conducting, whereinchanged in said electronic switch state cause a varying current in aninductive element, said current composed of charge extracted from astorage capacitor, said current applied to an output circuit, whereinsaid output circuit provides a steady output voltage in response to saidvarying current, an input device comprising: a resistor coupled betweensaid storage capacitor and an input power source, said resistor limitingcurrent flowing from said power source to said capacitor, and asilicon-controlled rectifier (SCR) coupled in parallel with saidresistor, a gate of said SCR coupled to said inductive element, whereinsaid varying current causes said SCR to assume a conducting state. 21.The circuit of claim 20 wherein said gate is coupled to said inductiveelement through a first control resistor and a diode and wherein saidgate is coupled to a cathode of said SCR through a capacitor and asecond control resistor, said capacitor and said second control resistorconnected in parallel, wherein said capacitor causes said SCR to remainin a conducting state for a preselected time after an alternation insaid state of said electronic switch, and wherein said first and secondcontrol resistors prevent excessive voltage between said gate and saidcathode.
 22. A circuit comprising: a storage capacitor; a limitingresistor coupled to said storage capacitor for limiting current flowinginto said storage capacitor; a switch element coupled in parallel withsaid limiting resistor, wherein activation of said switch element causessaid switch element to be in a conducting state, said conducting stateof said switch element providing an electrical path for by-passing saidlimiting resistor; and an inverter circuit for changing a DC signal toan AC signal, said inverter circuit coupled to said storage capacitor,wherein said storage capacitor provides said DC signal to said invertercircuit, said inverter circuit coupled to said switch element, whereinoperation of said inverter circuit causes said switch element to be insaid conducting state.
 23. The circuit of claim 22 wherein said switchelement includes a silicon-controlled rectifier, wherein a gate terminalof said SCR is coupled to said inverter circuit.
 24. The circuit ofclaim 23 wherein said switch element further comprises a capacitorcoupled between said gate terminal and a cathode terminal of saidsilicon-controlled rectifier, said capacitor providing biasing means formaintaining said switch element in a conducting state for a preselectedperiod of time after an operation of said inverter circuit.
 25. Thecircuit of claim 24 wherein said switch element further comprises afirst resistor coupled between said gate terminal and said cathodeterminal and wherein said switch element further comprise a secondresistor and a diode couple between said gate terminal and said invertercircuit.